Hi Drunkalot,
Microsoft has developed Rotor for research and education and it runs on BSD
Unix, Macintosh, and Windows:
http://www.sscli.net/servlets/ProjectList
Ximian, which has now been acquired by Novell, is working an independent
open source C#/CLI implementation called Mono:
http://www.go-mono.com
There is another independent project called DotGNU Portable.NET:
http://freshmeat.net/projects/pnet/
That's all the projects, other than .NET, I'm aware of at this time.
Joe